高温气固分离SiC多孔陶瓷材料制备及性能研究

本文利用等静压成型高温气固分离碳化硅多孔陶瓷支撑体,研究了碳化硅含量、造孔剂含量、成型压力及烧成温度对碳化硅多孔陶瓷支撑体孔隙率及抗折强度的影响。通过研究发现,碳化硅含量在88wt%、成型压力为40 MPa、烧成温度为1330℃时,制备的碳化硅支撑体性能较为理想,可用于工业化生产。     

高温气固分离碳化硅陶瓷支撑体成型压力研究

本文在保持显气孔率35%的前提条件下,研究了等静压成型的成型压力对高温气固分离碳化硅多孔陶瓷支撑体的强度、孔隙率和过滤压降的影响,同时研究了造孔剂含量与所需成型压力的关系。结果表明,在满足孔隙率的前提下,随着造孔剂含量的变化,成型压力也需相应地变化。当造孔剂含量为3 wt%、成型压力为40 MPa时,成型后坯体的强度、烧成后制品的强度和过滤压降均较理想。     

碳化硅含量对炭/陶复合导电材料组织和性能的影响

以长石、透辉石、石英等为陶瓷基料掺杂石墨、碳化硅,经湿混、干燥、干压成型、快速烧结等工艺制备了复合导电材料。测定了试样的气孔率、吸水率、烧成收缩率、烧失率以及抗弯强度,并分别用XRD和SEM分析晶相组成和断面显微结构,研究了碳化硅含量对复合材料电阻率的影响。实验结果表明:碳化硅的含量由1%增大到3%时,炭/陶复合导电材料的显微结构无显著变化,气孔率增大,烧成线收缩率降低,弯曲强度下降,电阻率变大;碳化硅含量由3%增大到9%时,炭/陶复合导电材料的陶瓷颗粒界面上形成一层白色碳化硅颗粒层,气孔率减小,弯曲强度增大,电阻率急剧降低;与碳化硅含量为1%的炭/陶复合导电材料相比,碳化硅含量增大到9%时,炭/陶复合导电材料孔隙率减小,弯曲强度增大,电阻率降低。     

Na2SO4-SiO2定形复合储能材料的制备及其性能

以无水硫酸钠和石英粉为主要原料制备了Na2SO4-SiO2复合储能材料。通过差热分析及成型压力、烧成温度和烧成保温时间对材料致密度、潜热、比热容的影响试验,确定了该材料的最佳制备工艺参数为:成型压力70 MPa,烧成温度950～1100℃,烧成保温时间90～150 min。对Na2SO4-SiO2复合储能材料的显微结构和性能进行了分析,结果表明:该储能材料由Na2SO4和SiO2两种物相组成,Na2SO4存在于SiO2陶瓷基体的微孔中;Na2SO4质量分数为50%的Na2SO4-SiO2复合储能材料在800～950℃的储能密度接近300 J.g-1,在950℃的热态耐压强度为4.3 MPa。     

低温烧结制备高气体渗透率的多孔碳化硅陶瓷研究

采用低温烧结法制备多孔碳化硅陶瓷,研究了成型压力、烧结温度等对其开气孔率、抗压强度、表面最大孔径和气体渗透率等的影响,通过SEM、EDS等表征其微观形貌和成分等。结果表明:在较低烧结温度850~950℃中烧成时,随着烧成温度的升高,多孔碳化硅陶瓷开气孔率和气体渗透率先增大后减小,体密度先减小后增大,表面最大孔径增加;抗压强度随开气孔率的增大而降低,压缩应力-应变表明多孔陶瓷的压溃分阶逐次进行,通过数次的局部压溃现象(应力台阶)来松弛主裂纹尖端的应力集中;随着成型压力的增加,其最大孔径和气体渗透率减小;在50 MPa成型870℃烧成时,多孔碳化硅陶瓷开气孔率达到38.4%,抗压强度80 MPa,表面最大孔径为12.86μm,气体渗透率达361.82m3/(m2·h·k Pa)。     

高炉炉身用碳化硅混凝土

砌筑高炉炉身通常采用粘土、碳化硅和其它耐火材料。为使砌筑过程机械化,采用捣打料和喷补料。采用不定形耐火材料取代整个制品,可以使材料生产的工艺过程机械化,同时,也可消除制品生产中很费力的成型、干燥、烧成、拣选和包装工序。除粘土材料外,抗熔渣熔融物和气体介质侵蚀能力高的含碳化硅材料得以广泛采用。     

工艺条件对发泡不饱和聚酯树脂密度和压缩强度的影响

通过调整成型温度、凝胶时间、固化时间和成型压力来确定发泡UPR材料最佳的成型工艺,探讨成型温度、凝胶时间、固化时间和成型压力四因素对发泡UPR材料综合性能的影响,实验结果表明:凝胶时间对低密度UPR的表观密度和压缩强度影响最大,固化时间对低密度UPR材料固化度的影响最大。实验最佳工艺参数为:成型温度为180℃、UPR胶液的凝胶时间为180s、固化时间为20min以及成型压力为1.0 MPa,制得的低密度UPR材料性能最佳。     

造孔剂法制备多孔生物玻璃陶瓷的工艺研究

通过造孔剂法,以溶胶-凝胶法制备的生物玻璃58S和熔融法制备的生物玻璃45S5为原料,以NH4 HCO3与淀粉的混合物为造孔剂制备生物玻璃陶瓷.利用XRD和SEM等材料分析测试手段研究了烧成温度、造孔剂添加量、成型压力及45S5的用量对多孔材料显微结构、表面形貌、抗折强度的影响.结果表明:在成型压力20 MPa,造孔剂含量60％,烧成温度800℃及45S5的加入量10％的工艺参数下,制备出抗折强度达到4.5 MPa,孔隙率达到68.74％的珊瑚状结构的多孔生物玻璃陶瓷材料.     

原位反应制备莫来石—氧化铝—碳化硅复相陶瓷材料的研究

本研究以氧化铝、碳化硅超细粉为原料,主要探讨了由原位反应制备莫来石—氧化铝—碳化硅复相陶瓷的反应原理与过程以及烧成温度、保温时间、颗粒细度与成形压力等工艺条件对碳化硅氧化反应的影响,并采用分段烧成制度制备了具有良好性能的复相陶瓷材料。     

不同烧结助剂对网眼碳化硅多孔陶瓷性能的影响

为了降低制备碳化硅网眼多孔陶瓷的烧结温度和制备成本,以聚氨酯泡沫为模板,分别以MgO-Al2O3-SiO2和K2O--Al2O3-SiO2为烧结助剂体系,采用浸渍成型制备低温烧成碳化硅网眼多孔陶瓷.采用X射线衍射、扫描电镜等测试手段对样品进行分析.结果表明:以MgO-Al2O3-SiO2体系为烧结助剂,当滑石的用量为1.8%(质量分数,下同)和3.8%时,样品的晶相组成是碳化硅、方石英、莫来石和堇青石,并且在显微结构中能看到针状莫来石晶体分布在玻璃相中和碳化硅晶粒的表面,针状莫来石晶体有利于材料强度的提高.以MgO-Al2O3-SiO2体系为烧结助剂,在1 350℃烧成的样品的抗压强度可达到1.23MPa.以K2O-Al2O3-SiO2体系为烧结助剂的样品中没有针状的莫来石晶体.     

Interfacial and thermomechanical characterization of reaction formed joints in silicon carbide-based materials

The microstructure and mechanical properties of reaction formed joints of Refel^TM reaction bonded SiC (RB-SiC) and Hexoloy^TM sintered SiC were studied in order to achieve a better understanding of the influence of base materials and joining process parameters on the high temperature strength of reaction formed joints. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and optical microscopy were used to characterize the joints prior to mechanical tests. The microstructural analysis indicated that the joints consist of silicon carbide (SiC) grains (with grain sizes ranging from 0.1 to 2 μm) and crystalline silicon as an intergranular phase. Most of the silicon carbide grains in the joint have hexagonal crystal structure with certain preferential orientations related to the silicon matrix. The high temperature strength of joints was measured by constant strain rate experiments in compression where joints were forming 45° with the compression axe. The strength of the joined Refel RB-SiC has been found to be at least equal to that of the bulk materials (550 MPa at 1235°C and 400 MPa at 1385°C). The joined Hexoloy specimens had strengths (1.4 GPa at 1290°C and 750 MPa at 1420°C) lower than the bulk material but higher than the joints of RB-SiC.     

The Role of Infiltration Temperature in the Reaction Bonding of Boron Carbide by Silicon Infiltration

The present paper is concerned on the effect of infiltration temperature on the components, microstructure, and mechanical properties of reaction‐bonded boron carbide (RBBC) ceramics. RBBC ceramics were fabricated by reactive infiltration of molten silicon (Si) into porous preforms containing boron carbide (B₄C) and free carbon. It has been found that infiltration temperatures have significant influence on the infiltration reactions involved and therefore the evolution of different phases formed in the RBBC ceramics. An increase in grain size of boron carbide particles through the coalescence of neighboring grains was observed at certain infiltration temperatures. The morphology of silicon carbide (SiC) phases developed from discontinuous and cloud‐like SiC to continuous and integrated SiC zones with the increase of infiltration temperatures. With increasing temperatures up to 1600°C, the hardness, flexural strength, and fracture toughness all increased. When the temperatures exceeded 1600°C, while the hardness and flexural strength decreased, the fracture toughness continued to increase.     

Tuning microstructures and separation behaviors of pure silicon carbide membranes

This study reports the preparation of silicon carbide ceramic membranes with pure silicon carbide particles without sintering aids. The effects of sintering temperature on the microstructure, mechanical and filtration properties were investigated. The porosity of the substrate layer increased from 37% to 41% when the sintering temperature ranged from 2150 to 2300 °C, whereas the flexural strength increased from 14.5 to 18.2 MPa. The separation layer was coated on the substrate layer using a spray process. When sintered at 1850 °C, a smooth and defect-free layer was formed with an average pore size and layer thickness of 1.2 and 60 μm, respectively. With the increase of average pore size, the filtration flux increased from 2650 to 2800 L/(m² h bar). Such ceramic membranes can be used to separate corrosive wastewater and high-temperature wastewaters owing to the exclusion of sintering aids, unlike the conventional ceramic membranes.     

Study of the physicomechanical properties of modified material of the composition Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiC–C based on acpb after reduction annealing

Dependences of the apparent density and ultimate strength in compression on amount of silicon carbide and form of modifying addition (Al, Si, B and other mixes) for materials of the composition Al2O3–SiC–C based on an aluminochromium phosphate binder after firing in a reducing atmosphere at 1400°C are studied. It is established that addition of amorphous boron and Al + Si + B are effective for improving physicomechanical properties.     

Tensile properties of two-dimensional carbon fiber reinforced silicon carbide composites at temperatures up to 2300 °C

Carbon fiber reinforced silicon carbide (C/SiC) composites are of the few most promising materials for ultra-high-temperature structural applications. However, the existing studies are mainly conducted at room and moderate temperatures. In this work, the tensile properties of a two-dimensional plain-weave C/SiC composite are studied up to 2300 °C in inert atmosphere for the first time. The study shows that C/SiC composite firstly shows linear deformation behavior and then strong nonlinear characteristics at room temperature. The nonlinear deformation behavior rapidly reduces with temperature. The Young’s modulus increases up to 1000 °C and then decreases as temperature increases. The tensile strength increases up to 1000 °C firstly, followed by reduction to 1400 °C, then increases again to 1800 °C, and lastly decreases with increasing temperature. The failure mechanisms being responsible for the mechanical behavior are gained through macro and micro analysis. The results are useful for the applications of C/SiC composites in the thermal structure engineering.     

Mechanical properties and microstructure of biomorphic silicon carbide ceramics fabricated from wood precursors

Silicon carbide-based, environment friendly, biomorphic ceramics have been fabricated by the pyrolysis and infiltration of natural wood (maple and mahogany) precursors. This technology provides an eco-friendly route to advanced ceramic materials. These biomorphic silicon carbide ceramics have tailorable properties and behave like silicon carbide based materials manufactured by conventional approaches. The elastic moduli and fracture toughness of biomorphic ceramics strongly depend on the properties of starting wood preforms and the degree of molten silicon infiltration. Mechanical properties of silicon carbide ceramics fabricated from maple wood precursors indicate flexural strengths of 344±58 MPa at room temperature and 230±36 MPa at 1350 °C. Room temperature fracture toughness of the maple based material is 2.6±0.2 MPa√m while the mahogany precursor derived ceramics show a fracture toughness of 2.0±0.2 MPa√m. The fracture toughness and the strength increase as the density of final material increases. Fractographic characterization indicates the failure origins to be pores and chipped pockets of silicon.     

Mechanical Characterization of Annealed ZrB2–SiC Composites

Composites consisting of 70 vol% ZrB₂ and 30 vol% α‐SiC particles were hot pressed to near full density and subsequently annealed at temperatures ranging from 1000°C to 2000°C. Strength, elastic modulus, and hardness were measured for as‐processed and annealed composites. Raman spectroscopy was employed to measure the thermal residual stresses within the silicon carbide (SiC) phase of the composites. Elastic modulus and hardness were unaffected by annealing conditions. Strength was not affected by annealing at 1400°C or above; however, strength increased for samples annealed below 1400°C. Annealing under uniaxial pressure was found to be more effective than annealing without applied pressure. The average strength of materials annealed at 1400°C or above was ~700 MPa, whereas that of materials annealed at 1000°C, under a 100 MPa applied pressure, averaged ~910 MPa. Raman stress measurements revealed that the distribution of stresses in the composites was altered for samples annealed below 1400°C resulting in increased strength.     

High‐Temperature Strength of Boron Suboxide Ceramic Consolidated by Spark Plasma Sintering

The spark plasma sintering (SPS) of B₆O ceramics using a highly crystalline boron suboxide powder with a low oxygen deficiency level is reported. The monolithic boron suboxide ceramic exhibited a room‐temperature strength of 300 ± 20 MPa, which is comparable to the strength of monolithic boron carbide. With increasing flexural test temperature, the strength of the boron suboxide ceramics increased to 450 MPa at 1400°C. The increase in strength with the temperature is associated with the unique microstructure of boron suboxide grains, which allows intergranular “brittle” fracture along subgrains even at 1400°C. This suggests that even higher strengths can be achieved.     

Properties of liquid phase pressureless sintered silicon carbide obtained without sintering bed

High density pressureless sintered silicon carbide bodies with yttria and alumina as sintering aids were obtained without sintering bed (LPSSC-NB). Sintering behavior of this material was studied between 1850 °C and 1950 °C and it was compared to the liquid phase sintered SiC material obtained using sintering bed (LPSSC-B). Sintered density was 97% of the theoretical density (T.D.) at 1875 °C. Mechanical properties like fracture toughness, hardness, flexural strength were determined and compared to other SiC-based materials. In this manner we were able to demonstrate that silicon carbide could successfully be sintered by means of liquid phase mechanism also without sintering bed. This fact opens liquid phase sintered silicon carbide to a wide range of industrial application.     

Lattice-structured SiC ceramics obtained via 3D printing,gel casting,and gaseous silicon infiltration sintering

In view of technical difficulties in preparing ceramics with complex shapes, gel casting combined with 3D printing was here adopted to prepare silicon carbide ceramic green body, and gaseous silicon infiltration sintering was used to prepare 3D lattice-structured ceramics. The preparation of the slurry, gel curing, and ceramic molding was investigated. Results demonstrate that the ratio of components affects the fluidity and stability of slurry. However, when volume fraction of the solid phase of the slurry reaches 56%, the viscosity of slurry is only 300 mPa s, and drying shrinkage rate of green body is 6.6%; these characteristics make slurry suitable for 3D complex model injection molding. Furthermore, both the temperature and the initiator affect gel curing speed. As the temperature and initiator content increase, the induction and gel time are rapidly shortened. When demolding at 300 °C and when gaseous silicon infiltration sintering is carried out at 1550 °C, a 3D lattice-structured ceramic with relative density of 87% and average compressive strength of 433 MPa can be obtained.